The sensitivity of intense rainfall to aerosol particle loading – acomparison of bin-resolved microphysics modelling withobservations of heavy precipitation from HyMeX IOP7a

Abstract. Over the Cevennes-Vivarais region in southern France five hour intensive rainfall covering an area of 1000 km2 with more than 50 mm rain accumulation was observed during IOP7a of HyMeX. This study evaluates the performance of a bin resolved cloud model for simulating this heavy precipitation event. The simulation results were compared with observations of rain accumulation, radar reflectivity, temporal and spatial evolution of precipitation, 5 minutes rain rates and raindrop size distributions (DSD). The different scenarios for aerosol number concentrations range from 1000 to 2900 cm−3 and represent realistic conditions for this region. Model results reproduce the heavy precipitation event with respect to maximum rain intensity, surface area covered by intense rain and the duration, as well as the rain DSD. Differences occur in the short-term rain fall rates, as well as for the drop number concentration. The cloud condensation number concentration has a notable influence on the simulated rainfall, both on the surface amount and intensity but also on the DSD properties and should be taken into account in microphysics parameterizations.